1. Field
The present disclosure relates to an ion exchange membrane, methods of manufacturing the ion exchange membrane, and redox flow batteries including the ion exchange membrane, and more particularly, to ion exchange membranes having excellent ion mobility and film properties, methods of manufacturing the ion exchange membrane, and redox flow batteries including the ion exchange membrane.
2. Description of the Related Art
A secondary battery is a highly efficient energy storage system which may be used for various devices ranging from small mobile apparatuses to medium to large scale energy storage systems. A redox flow battery as a secondary battery has received much attention due to its high output and durability that make it suitable for large scale power storage systems that provide high energy storage density.
Unlike other types of batteries, the redox flow battery includes an active material in a liquid state instead of a solid state and has a mechanism for generating and storing electrical energy through a redox reaction of ions in each of the catholyte and the anolyte. In other words, in the redox flow battery, the active material is dissolved in a solvent so that it is in solution, and when the redox flow battery including a catholyte and an anolyte having different oxidation numbers is charged, ions in the catholyte and anolyte solutions undergo an oxidation reaction and a reduction reaction at a contact surfaces of the cathode and the anode, respectively. An electromotive force of the battery can be determined by a difference in a standard electrode potential)(E° of the redox couple included the catholyte and the anolyte.
Also, the catholyte and the anolyte, which are in a liquid state in the redox flow battery, are separated by an ion exchange membrane disposed therebetween. In the redox flow battery, the ion exchange membrane does not directly participate in a reaction, but acts to (i) rapidly deliver ions, which are charge carriers, to a space between the catholyte and the anolyte, (ii) separate the cathode and the anode to prevent a direct contact between the cathode and the anode, and (iii) inhibit crossover between the electrolyte active ions that are dissolved in the catholyte and the anolyte and directly participate in the reaction.
An ion exchange membrane that has been used in the redox flow battery is aqueous. In other words, ion mobility and film properties of the ion exchange membrane are optimized in the redox flow battery using an aqueous electrolyte. However, when using an aqueous system, a driving potential of the aqueous redox flow battery is limited by a water splitting potential, and thus, a driving voltage and energy density of the aqueous redox flow battery are low. Thus, there is a need for an ion exchange membrane having ion mobility and film properties suitable for use in a non-aqueous redox flow battery.